Conventionally, an image capturing apparatus is provided with an image sensor to convert incident light to electric signals. Such the image sensor is capable of changing a conversion mode to the electric signals, based on intensity of the incident light. Concretely speaking, it is possible for such the image sensor to switchover the conversion mode between the linear conversion mode in which the incident light are linearly converted to the electric signals and the logarithmic conversion mode in which the incident light are logarithmically converted to the electric signals (for instance, set forth in Patent Document 1 and Patent Document 2).
According to the image sensor mentioned in the above, since the dynamic range of the electric signals can be widened, compared to that of another image sensor that can be operated only in the linear conversion mode, all of the luminance information can be represented by the electric signals, even when the subject to be captured has a wide luminance range.
In this connection, from the viewpoint for making the processing of the electric signals outputted from the image sensor easier, it is desirable that electric signals originated from a logarithmic conversion source (hereinafter, also referred to as electric signals of logarithmic conversion origin) are reconverted into those originated from a linear conversion source (hereinafter, also referred to as electric signals of linear conversion origin), so as to unify all of the concerned electric signals into those originated from the linear conversion source, and then, necessary processing are totally applied to the linearly-converted electric signals.
[Patent Document 1]                Tokkai 2002-77733, Japanese Non-Examined Patent Publication        
[Patent Document 2]                Tokkai 2004-88312, Japanese Non-Examined Patent Publication        